Filling level monitoring device for a fluid gas container, a hydrogen tank, and an aircraft comprising such a hydrogen tank

Abstract

Provided are a filling level monitoring device for a fluid gas container, a hydrogen tank, and an aircraft including such a hydrogen tank. **Solution**: A filling level monitoring device (100) for monitoring a filling level (210) of a fluid in a container (200) includes an exciter (10), a sensor (20), a signal source (30) connected to the exciter (10), a processor (40), at least one spatial orientation and acceleration sensor (60), and a filling level indicator (50). The device (100) uses the signal source (30) and the exciter (10) to couple a vibration load having a number of frequency components to the container (200). The sensor (20) measures vibrations in the container (200) after the exciter (10) transmits the vibration load to the container (200). The processor (40) performs a spectral analysis of an input signal (31) and a vibration signal (21) from the sensor (20), compares each of these spectral functions, and extracts a resonance frequency of the container (200) based on the spatial orientation of the container (200). The filling level indicator (50) calculates a current filling level (210) of the container (200) from the extracted resonance frequency and a spatial orientation signal from the spatial orientation sensor (60) by correlating the collected data with reference data.

Description

Technical Field

[0001] This disclosure relates to a fill level monitoring device for a fluid tank, and more particularly to a hydrogen tank for use in an aircraft having such a monitoring device.

Background Art

[0002] From the perspective of increasing environmental protection efforts, alternative propulsion sources for aircraft are being developed. Such alternative propulsion sources may use alternative fuels other than kerosene fuel that cannot be stored in conventional fuel tanks (e.g., liquid hydrogen). Therefore, it is necessary to store hydrogen fuel or other liquid gas fuels in a suitable tank that can withstand the necessary internal pressure and low temperature (e.g., about 20 K) required to store gas fuel in a liquid state. However, for safety reasons, regardless of the fuel type contained in such a fuel tank, it is also necessary to accurately monitor the fill level of the fuel tank at all times (e.g., in real time). Currently, the fill level of a fluid tank can be determined, for example, by measuring the weight of the tank or by indirectly monitoring the flow rate of the fuel exiting the tank. However, these methods may not be very accurate or may not be suitable for use in aircraft applications. An aircraft may, for example, be subject to altitude changes, and during the ascent or descent of the flight portion of the aircraft, the gravitational vector may not be constant with respect to the fuel tank, causing difficulties in determining the accurate weight value of the fuel tank and thus the accurate fill level of the fuel tank. The same applies to curved (e.g., non-linear) flight portions where the aircraft changes its flight vector.

Summary of the Invention

Problems to be Solved by the Invention

[0003] An object is to provide accurate monitoring of the fuel level of a fluid tank in an aircraft application.

Means for Solving the Problems

[0004] This object is solved by the subject matter disclosed herein.

[0005] According to a first aspect, there is provided a fill level monitoring device for monitoring the fill level of a container for a fluid. The fill level monitoring device includes at least one oscillator, at least one sensor, a signal source, a processor, at least one spatial orientation and acceleration sensor, and a fill level indicator. The at least one spatial orientation and acceleration sensor is connected to the processor and is configured to measure the spatial orientation of the fluid within the container. The signal source is connected to the at least one oscillator and is configured to generate an input signal including a number of frequency components. The at least one sensor is connected to the processor and is configured to detect vibrations in the container, generate a corresponding vibration signal, and transmit the vibration signal to the processor. The processor is configured to compare the vibration signal with the input signal and extract a resonance frequency. The fill level indicator is configured to receive the resonance frequency extracted from the processor and to receive the spatial orientation of the fluid within the container from the at least one spatial orientation and acceleration sensor. The fill level indicator is configured to determine the current fill level of the fluid within the container based on the extracted resonance frequency and the spatial orientation of the container.

[0006] Such a fill level monitoring device may be used for any container for a liquid, such as a gas bottle or a container for hydrogen. However, the fill level monitoring device is not limited to hydrogen containers. The fill level monitoring device may be used for a container for any other fluid stored under pressure in a liquefied form, such as liquefied petroleum gas (LPG), methane gas, or the like. Further, the fill level monitoring device may be used for a normal liquid tank. Generally, as used herein, the term fluid includes liquids (e.g., pressurized gas in liquid form), mixtures of liquids and gases, i.e., the fill of a container in which the fill of the container is present in both phase states (liquid and gas) simultaneously, and pure gases.

[0007] Generally, as any other specific structure, under force-based excitation, a container storing a fluid exhibits characteristic oscillation or rocking patterns where the amplitude of oscillation or vibration in a specific frequency range shows a maximum. Some of these so-called resonance frequencies depend only on the structure of the container itself and are independent of the filling of the container, while other resonance frequencies can be clearly assigned to the stored contents. In particular, a liquefied gas filling (e.g., liquid hydrogen) changes a specific resonance frequency of the container, and the change in frequency is proportional to the filling level of the container, i.e., the change in the mass and / or volume of the filling. Therefore, the filling level of the container may be accurately determined by monitoring the resonance frequency of the container.

[0008] The container may be, for example, a component of a tank (fluid) that actually holds the contents of the tank (e.g., a pressure-resistant gas bottle or other suitable structure). In particular, the container may have an axisymmetric shape, although other shapes are also conceivable.

[0009] The signal source, rather, the output terminal of the signal source, is connected to at least one exciter to generate an electrical signal having a predetermined signal pattern (e.g., an input signal for the exciter). In particular, the signal source generates an electrical signal that includes a number of different frequencies in the range of each resonance frequency corresponding to a frequency change at any possible filling level of the container. As described above, the specific resonance frequency of the filled container depends on the filling level of the container. Therefore, each filling level of the container has a characteristic pattern of resonance frequencies that directly corresponds to each filling level and may also depend on the spatial orientation of the fluid in the tank. The signal source may output, for example, a signal having a uniformly distributed spectral distribution (e.g., a white noise signal). However, other signal shapes including each frequency are also possible.

[0010] At least one exciter may be any element or device suitable for mechanically exciting the container, i.e., suitable for vibrating or rocking the container. In particular, the exciter may be mounted directly on the container and configured to vibrate in response to an electrical signal applied to the exciter. However, it is not always necessary to mount the exciter directly on the container, and the exciter may be, for example, a loudspeaker that emits sound waves or a similar device. In such a configuration, the emission direction of the speaker may be directed towards the container, and as a result, the emitted sound waves coupled to the container mechanically excite the container. Further, as will be described later, instead of an additional exciter, aircraft noise generated by a turbine, a pump, etc. may be directly coupled to the container and thus may function as an exciter. Since at least one exciter is connected to the output terminal of the signal source, the electrical signal output by the signal source (e.g., the input signal for the exciter) is converted by at least one exciter into each mechanical vibration or rocking coupled to the container. As will be readily apparent to those skilled in the art, the frequency component of the input signal corresponding to the resonance frequency of the container, rather the container and the fill system at a given time, exhibits the maximum relative amplitude of the rocking or vibration of the container, while other frequency components do not.

[0011] At least one sensor may be any detection or sensor element suitable for detecting the vibration or rocking of the container (or generally, changes in the structural dynamics of the container, or changes in the physical properties of the container wall that can be used because they are correlated with changes in the dynamics of the container), and generating each electrical signal (in particular, a signal including the frequency components of the rocking or vibration pattern of the container). These signals are input to the processor.

[0012] The at least one spatial orientation and acceleration sensor may be any sensor or sensor array capable of detecting the spatial orientation of the fluid within the container. Such a sensor or sensor array may in particular determine the orientation of the fluid within the container relative to any suitable coordinate system. In an aircraft application, for example, the spatial orientation and acceleration sensor may determine the orientation of the fluid within the container relative to the yaw, pitch and roll axes of the aircraft. The spatial orientation and acceleration sensor may be mounted directly on the container or may be part of, for example, the surrounding structure (e.g. the aircraft). Specifically, instead of individual spatial orientation and acceleration sensors mounted on the container, the signals of the yaw, pitch and roll axis sensors already present in the aircraft may be used to determine the orientation of the fluid within the container based on the determined orientation of the surrounding structure and the known relative orientation of the container with respect to the surrounding structure.

[0013] Furthermore, aircraft acceleration data obtained from the at least one spatial orientation and acceleration sensor, for example, considering the forces captured by a dense curve or other aerial maneuvers of the aircraft, may be considered. Furthermore, the corresponding forces cause a changing distribution of the fluid within the container and thus a change in the resonance frequency pattern.

[0014] Generally, the resonant frequency of a filled container may depend on the orientation of the fluid within the container with respect to the gravity and aircraft acceleration vectors. This is because when the container is oriented differently with respect to these vectors, the fluid within the container is stored at different orientations with respect to the container. Generally, the resonant frequency of a filled container changes depending on which regions of the inner wall of the container are in contact with the fluid. This is because a change in the orientation of the fluid within the container causes a change or shift in the resonant frequency. Thus, in particular, the measurement signals of a single sensor mounted at different positions on the container change with a change in the orientation of the fluid within the container. Further, a resonant frequency that did not show a shift in one orientation of the container may show a shift in a different orientation of the container, and vice versa. Thus, different resonant frequency patterns may occur, for example, at different flight orientations of an aircraft and at different acceleration states of the aircraft. This is, in particular, a result of the fluid within the container aligning with respect to the superposition of all forces acting on the aircraft that are captured by the gravity and the acceleration of the aircraft. As the aircraft ascends or descends, for example, the pitch angle of the container with respect to the gravity vector changes, and when sloshing propagates differently within the fluid in the container, it causes a shift in the fluid, and thus a shift in the resonant frequency. Further, as described above, aircraft acceleration data may be utilized. Specifically, different orientations of the fluid within the container cause different resonant modes due to changes in the structural dynamics of the container resulting from different distributions of the fluid within the container. By using one or more spatial orientation and acceleration sensors (perhaps together with sensor data from, for example, an aircraft acceleration sensor), these effects can be taken into account when determining the fill level of the container, as will be described later.

[0015] Furthermore, since the pressure inside the container changes with the change in temperature, the temperature of the container may be considered when determining the filling level. This may also cause a change in the resonant frequency of the container. For example, as described later, the temperature of the container may be explained in the same way as the accelerator by being included in the corresponding reference data or machine learning algorithm. Instead of or in addition to considering the temperature, the pressure inside the tank may be used directly. Therefore, the filling level monitoring system may further include corresponding temperature and / or pressure sensors.

[0016] Both the processor and the fill level indicator may be any computerized device capable of analyzing electrical signals, particularly by performing spectral or modal analysis. The unit may be, for example, a general-purpose computer having CPU and memory components well known in the art. Further, the unit may be any other microcomputer device (e.g., an ASIC or FPGA or TPU device). The processor receives an output signal (i.e., a vibration signal) from at least one sensor and executes a data analysis algorithm that calculates the frequency components of the signal received from the at least one sensor. Further, the processor receives and analyzes an input signal from a signal source and calculates the frequency components included in the input signal. However, instead of directly using the input signal, a sensor signal from a corresponding feedback sensor in the exciter may be used. For example, the frequency components of the input signal and the vibration signal may be determined by performing a fast Fourier transform (FFT) algorithm or any other spectral analysis algorithm on the input signal and the vibration signal, thereby generating a corresponding spectral function indicating the signal components over frequency. Next, the actual resonance frequency of the container may be determined or extracted, and thus, the spectral functions of the vibration signal and the input signal may be compared to generate an extracted resonance frequency. Such a comparison may be achieved, for example, by calculating a frequency response function (FRF) as further described below. Since the signal components having the resonance frequency of the container are amplified (as described above), other signal components are not amplified or are further attenuated, but these resonance frequencies (or resonance frequency patterns) can be estimated by comparing the spectral functions of the vibration signal and the input signal. Next, the extracted resonance frequency or resonance frequency pattern is passed to the fill level indicator.

[0017] The fill level indicator receives the extracted resonance frequency from the processor and receives the current spatial orientation of the fluid in the container from at least one spatial orientation and acceleration sensor. As described above, the spatial orientation of the fluid in the container affects the resonance frequency for a particular fill level. Thus, the fill level indicator takes into account the spatial orientation and acceleration of the container when determining the actual fill level of the container. For example, the fill level indicator may have a memory look-up table of resonance frequencies or resonance frequency patterns for every possible spatial orientation of the fluid in the container (or for a subset of such possible positions of interest). Further, if the fill level indicator also takes into account temperature and / or pressure data, it may have a memory look-up table of resonance frequencies or resonance frequency patterns for every possible temperature and / or pressure of the container. Next, for example, the actual fill level of the container may be determined by correlating or matching the extracted resonance frequency with a stored reference resonance frequency pattern. However, the fill level indicator may not use such a look-up table, but rather use a mathematical model of the structural dynamics of the container and calculate the corresponding reference resonance frequency pattern by correlating or matching the extracted resonance frequency with the model reference resonance frequency pattern. For this purpose, for example, a machine learning algorithm that takes into account the necessary parameters (such as spatial orientation and acceleration, and optionally temperature and / or pressure, etc.) may be utilized.

[0018] It should be noted that although the processor and the fill level indicator are described as two separate units, they can also be embodied as a common unit incorporating the functions of both units. Further, at least one spatial orientation and acceleration sensor may be connected to the processor, and the processor may calculate a reference resonance frequency or a reference resonance frequency pattern and pass those reference resonance frequencies to the fill level indicator. In such a configuration, the fill level indicator simply determines the actual fill level using the extracted resonance frequency and the reference resonance frequency received from the processor.

[0019] After determining the current filling level of the container, the filling level indicator may output a corresponding filling level signal that is passed, for example, to an on-board computer or other control and monitoring system.

[0020] According to an embodiment, at least one spatial orientation and acceleration sensor includes a first sensor that measures a pitch angle, a second sensor that measures a yaw angle, a third sensor that measures a roll angle of the container, and a fourth sensor that measures acceleration along the pitch axis, yaw axis, and roll axis. The spatial orientation is defined with respect to the pitch angle, yaw angle, and roll angle.

[0021] Such a spatial orientation and acceleration sensor is particularly advantageous in aircraft applications, especially when such sensors already exist in the aircraft. Thus, the signals of such sensors may be passed to the filling level monitoring device without the need to add additional sensors. However, at least one spatial orientation and acceleration sensor may be any position sensor suitable for determining the relative orientation of the fluid within the container with respect to the orientation of the container.

[0022] Furthermore, the filling level monitoring device may include an acceleration sensor or, as described above, use corresponding sensor data from the surrounding structure (e.g., an aircraft) to account for changes in the resonant frequency captured by acceleration. When using such an acceleration sensor together with a spatial position sensor, the sensor measures six degrees of freedom, namely, the spatial position with respect to each spatial axis and the corresponding acceleration with respect to each axis. In particular, when evaluating the filling level of the container by including an acceleration sensor, the superposition of gravity with such dynamic forces (e.g., forces captured by acceleration) may be considered.

[0023] According to another embodiment, at least one sensor is a device that can measure the dynamics of the container at the location of the sensor.

[0024] Such a device capable of measuring the dynamics of a container may be any device capable of detecting or measuring the characteristics of the container corresponding to the structural dynamics of the container (e.g., vibration or other suitable mechanical characteristics).

[0025] A device capable of measuring such characteristics may be, for example, a composite fiber strain gauge. Such a composite fiber strain gauge may consist of a rectangular piezoelectric ceramic rod sandwiched between an adhesive layer, electrodes, and a polyimide film. Electrodes are attached to the film in an interlocking pattern that transmits an applied voltage to and from the ribbon-shaped piezoelectric ceramic rod. This assembly is a sealed and durable package ready for use, enabling in-plane poling, actuation, and detection. The composite fiber strain gauge can be attached (usually bonded) as a thin surface conforming plate to various types of structures, or incorporated into composite structures. When a voltage is applied, the composite fiber strain gauge acts as an actuator, bending or deforming the material, preventing vibration, or generating vibration. When no voltage is applied, the composite fiber strain gauge can act as a highly sensitive strain gauge that detects deformation, noise, and vibration. Thus, when the container vibrates or sways, small deformations of the container are detected by the composite fiber strain gauge. Since the vibration of the container contains specific frequency components, the output signal of the composite fiber strain gauge follows the frequency pattern of the vibration.

[0026] According to another embodiment, at least one exciter is attached to the container and configured to couple a vibration load corresponding to an input signal from a signal source to the container.

[0027] For this purpose, at least one exciter may be any device that can couple a vibration load or other mechanical load to the container. By way of non-limiting example, the exciter may be a piezoelectric element. Such piezoelectric elements are well known in the art. When a voltage is applied to such an element, the piezoelectric element deforms in response to the electrical signal (reverse piezoelectric effect). Thus, when an irregular signal is applied, the piezoelectric element begins to vibrate in response to the frequency components of the input signal, thereby coupling the corresponding vibration load to the container. Such a piezoelectric element may be, for example, of the same type as the composite fiber strain gauge described above with respect to at least one sensor.

[0028] However, any other conceivable exciter may be used.

[0029] According to another embodiment, the signal source is configured to generate a signal suitable for obtaining a frequency response function (FRF) in a desired frequency range as an input signal.

[0030] Thus, the signal may be any signal that includes the frequency range necessary or desirable for monitoring the resonant frequency of the container suitable for obtaining the frequency response function, as will be described further below.

[0031] By way of non-limiting example, such a signal may be a white noise signal. As is known in the art, such a white noise signal is a statistically irregular signal having equal intensity at different frequencies. Thus, when such a white noise signal is used as the input signal, a wide range of evenly distributed frequency components are coupled to the container, and only the vibration at the current resonant frequency of the container exhibits a maximum amplitude. By using an appropriate window function (e.g., a Gaussian window or a rectangular window), the input signal may be restricted to a specific input frequency range.

[0032] However, any other input signal that includes the possible resonant frequencies of the container at different filling levels may be used.

[0033] According to another embodiment, the processor is configured to compare the vibration signal with the input signal by calculating the fast Fourier transform (FFT) of the vibration signal and the input signal and comparing the FFT of the vibration signal with the FFT of the input signal.

[0034] However, as will be readily apparent to those skilled in the art, other spectral or modal analysis algorithms may be used.

[0035] According to another embodiment, the processor is configured to extract the resonance frequency by calculating the frequency response function (FRF) of the vibration signal with respect to the input signal using the FFT of the vibration signal and the FFT of the input signal, thereby obtaining a pattern of resonance frequencies.

[0036] Such a frequency response function is defined as follows.

Equation

[0037] According to another embodiment, the fill level indicator is configured to determine the current fill level of the container based on the extracted resonance frequency by correlating the acquired pattern of resonance frequencies with the calibrated pattern of resonance frequencies.

[0038] Although described as being determined by correlating the acquired pattern of resonance frequencies with the calibrated pattern, the fill level may be determined by tracking a single resonance frequency (particularly, the resonance frequency that exhibits a strong correlation with the fill level) over time. Such a single resonance frequency may be proportional to the fill level for a given period of time.

[0039] The calibration pattern may be determined, for example, by controlled discharge of the container in a laboratory or operating environment, thereby determining the resonance frequency pattern of the container for different filling levels and different spatial orientations. The resonance frequencies thus determined may be stored, for example, in a matrix that is one-dimensional or multi-dimensional. For example, such a matrix can be four-dimensional when using three spatial orientation sensors (e.g., for yaw, pitch, and roll). One dimension of the matrix can correspond, for example, to the filling level, the second dimension can correspond to yaw, the third dimension can correspond to pitch, and the fourth dimension can correspond to roll. Next, during operation, the filling level of the container may be determined by correlating the extracted reference frequency with the corresponding matrix element taking into account the estimated spatial orientation of the fluid in the container.

[0040] According to another embodiment, the filling level monitoring device is configured to determine the current filling level of the container based on the extracted resonance frequency or FRF by means of machine learning and artificial intelligence methods trained with the calibration pattern or FRF of the resonance frequency as input using the acquisition pattern or FRF of the resonance frequency.

[0041] According to another embodiment, the calibration pattern or FRF of the resonance frequency includes the calibration pattern or FRF of the resonance frequency for different spatial orientations of the fluid in the container. The filling level indicator is configured to be trained by machine learning and artificial intelligence methods with the calibration pattern or FRF of the resonance frequency and the acquisition pattern or FRF of the resonance frequency as input to select the calibration pattern of the resonance frequency corresponding to the current spatial orientation of the fluid in the container before determining the current filling level of the container.

[0042] According to another embodiment, the calibration pattern of the resonance frequency includes the calibration pattern of the resonance frequency for different spatial orientations of the fluid in the container, and the filling level indicator is configured to select the calibration pattern of the resonance frequency corresponding to the current spatial orientation of the fluid in the container before determining the current filling level of the container.

[0043] However, instead of using memory reference data (e.g., calibration patterns), the corresponding reference data may be calculated "on the fly" by using a computer model of the structural dynamics of the container or other means. For example, the selection mode may be tracked over time, or an algorithm based on artificial intelligence (e.g., a machine learning algorithm) may be used.

[0044] According to a second aspect, a hydrogen tank is provided. The hydrogen tank includes a container for holding liquefied hydrogen and a filling level monitoring device.

[0045] The filling level monitoring device may be embodied according to any one of the above-described embodiments and is configured to monitor the filling level of the container of the hydrogen tank according to the above-described principles.

[0046] According to a third aspect, an aircraft is provided. The aircraft includes an aircraft fuselage, an aircraft turbine, and a hydrogen tank. The hydrogen tank is fixedly positioned in place with respect to the aircraft fuselage. At least one spatial orientation and acceleration sensor is a spatial orientation and acceleration sensor of the aircraft itself.

[0047] Such an aircraft may use hydrogen as an alternative fuel, i.e., use hydrogen as an energy source to drive the turbine. For example, hydrogen may be used as a primary energy source by directly burning hydrogen in the turbine, or, for example, by using a hydrogen fuel cell to generate electrical energy and supplying power to the turbine with the thus-generated electrical energy, hydrogen may be used as a secondary energy source.

[0048] The hydrogen tank filling level monitoring device according to the present disclosure enables accurate monitoring of the filling level of a hydrogen tank under any flight conditions. By fixing the hydrogen tank to the fuselage, the spatial orientation of the liquid hydrogen in the tank relative to the orientation of the tank may be determined using the aircraft's spatial orientation and acceleration sensors (e.g., pitch, yaw, and roll axis sensors). The container of the hydrogen tank may be positioned within the fuselage such that, for example, the longitudinal axis of the container coincides with the longitudinal axis of the fuselage. In this way, the pitch movement of the aircraft corresponds to, for example, the "pitch" movement of the container. Accordingly, the aircraft's coordinate system may be used directly for the container.

[0049] According to an embodiment, the filling level monitoring device is configured to monitor the hydrogen filling level of the container.

[0050] In particular, the filling level monitoring device may constantly monitor the filling level during flight and report the corresponding filling level to the pilot.

[0051] According to an embodiment, a source of vibration within the aircraft suitable for exciting the container within a desired frequency range is the signal source of the filling level monitoring device.

[0052] Such a vibration source may be any vibration source within the aircraft. The vibration of such a vibration source may be coupled to the container and may serve as the excitation source for the filling level monitoring device.

[0053] According to another embodiment, the source of vibration within the aircraft is an aircraft turbine.

[0054] During operation, an aircraft turbine generates specific frequency components in the form of vibrations or electromagnetic noise. These noise or vibration signals may include a frequency range wide enough to include the resonant frequency range of the hydrogen tank's container for different filling levels, such that no additional signal source is required. Instead, the vibrations of the turbine may be directly coupled to the container, or the electromagnetic noise may be collected and transmitted to at least one exciter, for example, by using an antenna or other signal collection techniques. In the first case, no additional exciter and no additional signal source are required. In the second case, only an exciter is required and no additional signal source is needed. However, it should be noted that an aircraft turbine is only one example of a vibration source that can be used in a filling level monitoring system, and any vibration source within an aircraft can be used as an excitation source for determining the filling level of the container. Thus, the vibration source is not limited to an aircraft turbine.

[0055] In short, the present disclosure provides an accurate monitoring system for tracking the filling level of a fluid tank (e.g., a liquid hydrogen tank). Due to the changing flight conditions of an aircraft (and the cryogenic nature of LiH 2 ), conventional filling level monitoring techniques, such as measuring the fluid flowing out of the tank or determining the weight of the tank, are inherently inaccurate. By measuring the filling level of the fluid tank by monitoring the filling level-dependent resonant frequency, and in particular by further considering the spatial orientation of the fluid within the tank during changing flight conditions (e.g., ascending or descending flight), these inaccuracies can be avoided. Thus, the present disclosure generally enables more accurate non-invasive monitoring of the filling level of a fluid tank, thereby enhancing the safety of an aircraft using alternative fuels (e.g., hydrogen).

[0056] It should be noted that although the present disclosure is described in the context of aircraft applications, the disclosure can be used in any suitable application (e.g., automotive and similar applications).

[0057] Hereinafter, examples of embodiments will be described in more detail with reference to the accompanying drawings. The illustrations are schematic and not to scale. The same reference numerals denote the same or similar elements.

Brief Description of the Drawings

[0058]

Figure 1

Figure 2

Figure 3

Mode for Carrying Out the Invention

[0059] FIG. 1 schematically shows an example of an embodiment of a liquid hydrogen tank indicated as 300 as a whole. The hydrogen tank 300 includes a container indicated as 200 as a whole and a filling level monitoring device indicated as 100 as a whole. In the illustrated configuration, the filling level monitoring device 100 includes one or more (for example, two or more) exciters 10 and one or more (for example, eight or more) sensors 20. Further, the filling level monitoring device 100 includes a signal source 30, a processor 40, a filling level indicator 50, and a spatial orientation and acceleration sensor 60. The exciter 10 is electrically connected to the signal source 30. The processor 40 is electrically connected to the filling level indicator 50. The signal source 30 is electrically connected to the processor 40, the sensor 20 is electrically connected to the processor 40, and the spatial orientation and acceleration sensor 60 is electrically connected to the filling level indicator 50.

[0060] The container 200 contains liquid hydrogen therein, and the filling level of the liquid hydrogen is schematically indicated by the filling level 210. The container 200 is a pressure-resistant gas container configured to hold pressurized liquefied hydrogen gas.

[0061] As described elsewhere herein, signal source 30 may be any signal source that generates an electrical signal containing a number of frequency components. The frequency range in which signal source 30 can generate one or more input signals extends to the possible resonance frequencies of container 200 at different filling levels 210. This frequency span of the resonance frequency of container 200 based on the filling level 210 of liquid hydrogen here may be determined, for example, by computer simulation of the structural dynamics of container 200. Further, the frequency span may be determined in advance in a laboratory environment for easy understanding. In the illustrated configuration, signal source 30 is a Gaussian white noise signal source 30 configured to generate a wide range of evenly distributed frequency components.

[0062] Container 200 has various resonance frequencies, some of which are merely correlated with the structural dynamics of container 200 itself, while other resonance frequencies depend on filling level 210. In particular, some of the resonance frequencies are proportional to the filling level 210 of container 200 and shift when the filling level 210 in container 200 changes. Therefore, the filling level 210 of container 200 may be accurately determined by monitoring the shift of the resonance frequency of container 200.

[0063] Gaussian white noise signal source 30 is configured to generate a corresponding electrical signal or input signal 31 transmitted to exciter 10. Exciter 10 may be any element or device capable of generating mechanical rocking or vibration. In the illustrated configuration, for example, exciter 10 is a piezoelectric element directly attached to container 200 and using the inverse piezoelectric effect, thereby generating vibrations corresponding to input signal 31 from signal source 30 coupled to container 200 by exciter 10. However, exciter 10 may be any other device capable of coupling mechanical vibrations to container 200, and in particular, may not be directly attached to container 200. For example, exciter 10 may be a sound wave source directed at container 200. However, the foregoing description of exciter 10 is merely an example, and in principle, any other suitable device may be used for exciter 10.

[0064] During measurement, the oscillation or vibration from the exciter 10 corresponding to the resonance frequency of the container 200 with respect to the filling level 210 is amplified within the container 200, generating corresponding vibrations within the container 200, while other frequency components are not amplified.

[0065] Next, the sensor 20 is configured to collect or measure these vibrations of the container 200 and generate a corresponding vibration signal 21 that is transmitted to the processor 40. The sensor 20 may be any sensor 20 capable of measuring oscillation or vibration within the container 200. In the illustrated example of the embodiment, the sensor 20 is a composite fiber strain gauge consisting of an insulating flexible backing formed from a composite fiber material supporting a metal foil pattern. The gauge may be attached to the container 200 (e.g., using a suitable adhesive). When the container 200 vibrates or oscillates, a small deformation of the container 200 deforms the metal foil of the sensor 20, thereby changing the electrical resistance of the sensor 20. This change in resistance may be measured, for example, using a Wheatstone bridge. Since the vibration of the container 200 contains specific frequency components, the change in the resistance of the fiber strain gauge follows the frequency pattern of the vibration. However, other suitable sensors may be used. For example, the sensor 20 may be a piezoelectric element attached to the container 200 (e.g., the exciter 10) that generates an electrical signal corresponding to the mechanical load coupled to the piezoelectric element from the container 200.

[0066] Although two exciters 10 and eight sensors 20 are shown and described, it should be noted that any other quantity of exciters 10 and sensors 20 may be used depending on the specific requirements of a particular application. Generally, increasing the quantity of exciters 10 and the quantity of sensors 20 allows more data to be correlated, thus increasing the accuracy of the filling level measurement.

[0067] Processor 40 may be any computing device that processes signals, such as a general-purpose computer having a CPU and memory components, a microcomputer, an FPGA, an ASIC, a TPU, or any combination thereof, or any other suitable computing device. Processor 40 receives the vibration signal 21 from sensor 20 and further receives the input signal 31 from signal source 30. By comparing the input signal 31 with the vibration signal 21, processor 40 can extract the resonance frequency of container 200 for the corresponding filling level 210. Processor 40 may perform spectral or modal analysis, for example, by calculating the fast Fourier transform (FFT) of the input signal 31 and the vibration signal 21. By comparing the obtained spectral functions, the resonance frequency may be easily extracted as will be readily understood by those skilled in the art. For example, processor 40 may calculate the frequency response function (FRF) from the spectral functions of the input signal 31 and the vibration signal 21. Such a frequency response function is defined as follows. [Number]

[0068] In this equation, H(f) is the frequency response function representation for the amplification of the amplitude of a specific frequency component over frequency f, V(f) is the vibration signal over frequency (e.g., the FFT of input signal 31), and I(f) is the input signal over frequency (e.g., the FFT of vibration signal 21). Since the vibration of container 200 at the corresponding resonance frequency is amplified, the frequency response function H(f) thus obtained has a maximum at the resonance frequency. FIG. 2 shows an example of such an exemplary FRF, as will be described further below. The obtained frequency response function is transmitted to the filling level indicator 50.

[0069] The fill level indicator 50 determines the current fill level 210 of the container 200 by comparing the corresponding resonance frequency pattern known for the container 200 for different fill levels 210 with the extracted resonance frequency (e.g., FRF from the processor 40). The fill level indicator 50 may have, for example, a memory look-up table of frequency response functions or resonance frequency patterns for different fill levels 210. The current fill level of the container 200 may be obtained by correlating the stored reference data with the determined FRF (or generally, the extracted resonance frequency).

[0070] Since the resonance frequency of the container 200 also depends on the spatial orientation of the fluid within the container 200 relative to the spatial orientation of the container 200, as further described above, the spatial orientation and acceleration sensor 60 determines the spatial orientation of the fluid within the container 200 relative to the gravity vector and transmits the corresponding spatial orientation data to the fill level indicator 50. The fill level indicator 50 may use the spatial orientation data to select the corresponding reference resonance frequency pattern before comparing the extracted resonance frequency or resonance frequency pattern with the reference data. For example, the reference resonance frequency values may be stored in a multi-dimensional matrix as described elsewhere herein, and the fill level indicator 50 may select the corresponding value for the current spatial orientation from this matrix before determining the fill level 210.

[0071] Instead of using the stored reference data, the fill level indicator 50 may calculate the corresponding reference values "on the fly" by using a computer model of the structural dynamics of the container 200.

[0072] After determining the current fill level 210 of the container 200, the fill level indicator 50 outputs a fill level signal 51 that can be transmitted, for example, to a control system or a display device. In an aircraft application, the fill level signal may be transmitted to a flight control computer or a display device in the aircraft cockpit.

[0073] Figure 2 shows an example of a plot of the frequency response function as described with respect to Figure 1, which is obtained during a continuous discharge test. In such a continuous discharge test, the container 200 of the hydrogen tank 300 is discharged by the control method, and the frequency response function is determined according to the principle described herein. Figure 2 shows different frequency response functions for different filling levels 210. It can be seen that the resonance frequency of the container 200 shifts with the change of the filling level 210 of the container 200. Resonance peaks for four different filling levels 210, namely 100%, 93%, 50% and 0% are shown. Such a reference frequency response function may be determined in advance for different spatial orientations of the fluid within the container 200. The filling level indicator 50 of Figure 1 may use such a frequency response function determined in a laboratory environment as reference data for determining the filling level 210. However, such reference data may also be calculated by a structural dynamics model as described above.

[0074] Figure 3 shows an example of an embodiment of an aircraft 400 having a fuselage 410 and two turbines 420. Further, the aircraft includes, for example, a liquid hydrogen tank 300 as described above with respect to Figure 1. The hydrogen tank 300 functions as a fuel source for the turbines 420. The turbines 420 may directly combust hydrogen from the hydrogen tank 300 as a primary energy source, or may be electric turbines using electrical energy generated, for example, by a fuel cell that consumes hydrogen from the hydrogen tank 300.

[0075] In this example of the embodiment, the vibration of the turbine 420 is directly coupled to the container 200 of the hydrogen tank 300. Thus, the turbine 420 itself functions as an exciter 10 with respect to the container 200 and couples the vibration to the container 200.

[0076] Furthermore, the yaw sensor, pitch sensor, and roll sensor of the aircraft itself are connected to the fill level indicator 50 and function as the spatial orientation and acceleration sensor 60 of FIG. 1. The tank is fixed in place within the fuselage 410. Thus, no additional spatial orientation and acceleration sensors (e.g., see 60, FIG. 1) are required, and existing sensors within the aircraft 400 can be used. Further, since the turbine 420 itself functions as the exciter 10 for the fill level monitoring device 100 of the hydrogen tank 300, no additional exciter 10 is required.

[0077] By including the spatial orientation data of the container 200 in the fill level monitoring device 100, the fill level 210 of the hydrogen tank 300 can be accurately monitored for aircraft applications, particularly during any flight condition.

[0078] It should be noted that "comprising" or "including" does not exclude other elements or steps, and "one" or "a" does not exclude a plurality. Further, it should be noted that the features or steps described with respect to any of the above embodiments can also be used in combination with the other features or steps of the other above embodiments. The reference signs in the claims should not be regarded as limiting.

[0079] The subject matter disclosed herein can be implemented in software or with software in combination with hardware and / or firmware. For example, at least a portion of the subject matter described herein can be implemented in or with software executed by a processor or processing unit. In one example of an implementation, a computer-readable medium having computer-executable instructions (stored on a computer-readable medium) that control a computer to perform steps when executed by a processor of the computer can be used to implement the subject matter described herein. Examples of computer-readable media suitable for implementing the subject matter described herein include non-transitory devices (e.g., disk memory devices, chip memory devices, programmable logic devices, and application specific integrated circuits). Further, the computer-readable media for implementing the subject matter described herein can be disposed on a single device or computing platform, or can be distributed across a number of devices or computing platforms.

[0080] Although at least one example of an embodiment of the present invention is disclosed herein, modifications, substitutions, and alternatives will be apparent to those skilled in the art and are to be considered executable without departing from the scope of this disclosure. This disclosure is intended to include any adaptations or variations of the examples of the embodiments. Further, in this disclosure, the terms "comprise" or "comprising" do not exclude other elements or steps, the terms "a", "an", or "one" do not exclude a plurality, and the term "or" means either or both. Further, the described features or steps can be used in any order in combination with other features or steps, unless the disclosure or context suggests otherwise. Thereby, this disclosure incorporates by reference the complete disclosure of any patent or application for which benefit or priority is claimed.

Description of the Reference Numerals

[0081] 10 Vibrator 20 Sensor 21 Vibration signal 30 Signal source 31 Input signal 40 Processing unit 50 Filling level indicator 51 Filling level signal 60 Spatial orientation and acceleration sensor 100 Filling level monitoring device 200 Container 210 Filling level 300 Hydrogen tank 400 Aircraft 410 Fuselage 420 Turbine

Claims

1. A fill level monitoring device (100) for monitoring the fill level (210) of a fluid in a container (200), comprising: at least one exciter (10); at least one sensor (20); a signal source (30) connected to the at least one exciter (10) and configured to generate an input signal (31) including a plurality of frequency components; a processor (40); at least one spatial orientation and acceleration sensor (60); and a fill level indicator (50). The at least one spatial orientation and acceleration sensor (60) is connected to the fill level indicator (50) and is configured to measure the spatial orientation of the fluid in the container (200). The at least one sensor (20) is connected to the processor (40), detects vibration in the container (200), generates a vibration signal (21) corresponding to the detected vibration based on the vibration detected in the container (200), and transmits the vibration signal (21) to the processor (40). The processor (40) is configured to compare the vibration signal (21) with the input signal (31) and extract a resonance frequency. The fill level indicator (50): receives the extracted resonance frequency from the processor (40); receives the spatial orientation of the fluid in the container (200) from the at least one spatial orientation and acceleration sensor (60); and determines the current fill level (210) of the container (200) based on the extracted resonance frequency and the spatial orientation of the fluid in the container (200). The fill level monitoring device (100) is configured as such.

2. The at least one spatial orientation and acceleration sensor (60) includes: a first sensor configured to measure a pitch angle; a second sensor configured to measure a yaw angle; a third sensor configured to measure a roll angle; and a fourth sensor configured to measure an acceleration along each spatial orientation axis of the container (200). The spatial orientation is defined with respect to the pitch angle, the yaw angle, the roll angle, and the acceleration for each spatial orientation. The fill level monitoring device (100) according to Claim 1.

3. ​ ​ ​ The filling level monitoring device (100) according to claim 1 or 2, wherein the at least one sensor (20) is configured to measure the vibration dynamics of the container (200) at the position of the at least one sensor (20).

4. The filling level monitoring device (100) according to any one of claims 1 to 3, wherein the at least one exciter (10) is mounted on the container (200) and configured to couple a vibration load corresponding to the input signal (31) from the signal source (30) to the container (200).

5. The filling level monitoring device (100) according to any one of claims 1 to 4, wherein the signal source (30) is configured to generate a signal suitable for obtaining a frequency response function (FRF) in a desired frequency range as the input signal (31).

6. The filling level monitoring device (100) according to any one of claims 1 to 5, wherein the processor (40) calculates a fast Fourier transform (FFT) of each of the vibration signal (21) and the input signal (31), and compares the FFT of the vibration signal (21) with the FFT of the input signal (31) to compare the vibration signal (21) with the input signal (31).

7. The filling level monitoring device (100) according to claim 6, wherein the processor (40) calculates a frequency response function (FRF) of the vibration signal (21) with respect to the input signal (31) using the FFT of the vibration signal (21) and the FFT of the input signal (31), and thereby extracts the resonance frequency by obtaining a pattern of the resonance frequencies.

8. The filling level monitoring device (100) according to claim 7, wherein the filling level indicator (50) is configured to determine the current filling level (210) of the container (200) based on the extracted resonance frequency or FRF by correlating the obtained pattern of the resonance frequencies or FRF with a calibration pattern of the resonance frequencies.

9. The filling level indicator (50) determines the current filling level (210) of the container (200) based on the extracted resonance frequency or FRF by machine learning and artificial intelligence methods trained with the calibration pattern or FRF of the resonance frequency using the pattern or FRF of the acquired resonance frequency as an input. The filling level monitoring device (100) according to claim 7.

10. The calibration pattern or FRF of the resonance frequency includes the calibration pattern or FRF of the resonance frequency for different spatial orientations of the fluid in the container (200). The filling level indicator (50) is configured to be trained by machine learning and artificial intelligence methods with the calibration pattern or FRF of the resonance frequency and the acquired pattern or FRF of the resonance frequency as inputs to select the calibration pattern of the resonance frequency corresponding to the current spatial orientation of the fluid in the container (200) before determining the current filling level (210) of the container (200). The filling level monitoring device (100) according to claim 8.

11. The calibration pattern or FRF of the resonance frequency includes the calibration pattern or FRF of the resonance frequency for different spatial orientations of the fluid in the container (200). The filling level indicator (50) is configured to select the calibration pattern or FRF of the resonance frequency corresponding to the current spatial orientation of the fluid in the container (200) before determining the current filling level (210) of the container (200). The filling level monitoring device (100) according to claim 8.

12. Including a display, the filling level indicator (50) is configured to transmit a filling level signal (51) to the display. The filling level monitoring device (100) according to any one of claims 1 to 11.

13. The filling level indicator (50) is configured to transmit a filling level signal (51) to the flight control computer of the aircraft (400). The filling level monitoring device (100) according to any one of claims 1 to 12.

14. A container (200) for holding liquefied hydrogen, At least one filling level monitoring device (100) according to any one of claims 1 to 13 And a hydrogen tank (300) including.

15. An aircraft fuselage (410), An aircraft turbine (420), at least one hydrogen tank (300) according to claim 14, and comprising the hydrogen tank (300) is fixedly positioned in place relative to the aircraft fuselage (410), the at least one spatial orientation and acceleration sensor (60) is a spatial orientation and acceleration sensor (60) of the aircraft (400) itself, aircraft (400). **Claim 16** The aircraft (400) according to claim 15, wherein the filling level monitoring device (100) is configured to monitor the filling level (210) of liquefied hydrogen in the container. **Claim 17** The aircraft (400) according to claim 15, wherein the signal source (30) of the filling level monitoring device (100) is a source of vibrations within the aircraft (400) suitable for exciting the container (200) in a desired frequency range.

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